1. Field of the Invention
This disclosure relates to exercise devices, such as treadmills, particularly to treadmills which utilize a motor and arm movement of a user together to drive the belt.
2. Description of the Related Art
Conventional treadmills operate by employing a motor to rearwardly drive an endless belt upon which the user runs, walks, or otherwise engages in ambulatory leg movement, generally in a direction opposing the motion of the belt. As the user is moving in opposition to the belt, the user therefore exercises in order to remain in place. Generally, a user of a conventional treadmill is able to vary the speed and incline of the treadmill to obtain a desired level of workout by increasing the speed of the motor to accelerate the speed of the belt and increase their necessary movement speed. Alternatively, the user can make the workout more difficult by increasing the incline to simulate moving uphill. More sophisticated motorized treadmills, such as those described in U.S. Pat. No. 5,462,504, the entire disclosure of which is herein incorporated by reference, automatically adjust the speed and incline of the treadmill to control the heart rate of the user during the exercise.
Conventional treadmills of this type function to exercise the user's cardiovascular system and the skeletal muscles of the lower body, but do not exercise the upper body to any significant extent. However, a number of treadmills have been constructed which have upper body exercise devices associated therewith. These upper body exercise systems are traditionally arm members which are independently moveable against the resistance of a spring or friction plate in a swinging motion, to provide for an upper body workout in conjunction with the cardiovascular and lower body workout while still providing a fairly natural movement.
There are also simple treadmills which do not use motors to supply the belt's rotary motion, but instead rely on the user of the treadmill to provide their own motion which is imparted to the belt. These devices have a clear advantage over motorized units in being significantly lighter than their motorized counterparts, and generally much less expensive to produce. To allow for continuous, in-place, motion, non-powered or “motorless” treadmills traditionally were designed to support the endless belt on an incline such that the belt rotates rearwardly as a result of the weight and forward stride of the user overcoming belt friction. However, once the incline is set, these types of treadmills can feel unnatural to a user because changes to the belt speed depend only upon the amount of additional rearward force a user is able to apply. A faster running movement is unlike actual running as the stride must be changed to impart sufficient force to the belt to generate the speed of the belt necessary for the running movement as it is not supplied externally by the motor. For example, without interrupting an exercise session to adjust the incline, a user wishing to increase the speed of a gravity-driven belt must push down and/or forwardly on hand rails or arm members in order to change the amount of rearward force applied to the belt. Such a motion is not a natural change to a person's stride when increasing speed.
Further, traditional motorless treadmills cannot effectively use both incline and speed to independently alter exercise characteristics because the weight of the user, incline and speed are all related. Therefore, when the incline is increased, the speed also increases. While in some cases this may be desirable, in many cases it is not. In particular, many desirable cardiovascular workouts use periods of walking on high inclines followed by periods of running on low inclines. This type of exercise cannot be performed on traditional motorless treadmills because as the incline is increased, the user necessarily must move faster based on the design of the machine.
U.S. Pat. Nos. 5,688,209 and 5,871,421, the entire disclosures of which are herein incorporated by reference, describe motorless treadmills which allow the user to supplement the motion of the belt with the motion of their arms to eliminate or reduce some of the issues of being unable to control speed and incline separately. These treadmills provide both an upper and lower body workout as they provide for upper body power being transferred to the rotation of the belt. These treadmills also help to eliminate the need to use unnatural motions to produce different speeds which improves the natural feeling of the exercise motion and helps to provide separate control over incline and speed. If a user wishes to go faster, they can increase the speed of the belt by increasing the rate (or power) applied to the arm members which accelerates the belt without the user having to alter their stride in an unnatural fashion or stop the exercise and alter the incline of the belt.
While these devices are an improvement over what was previously available as they allow for, among other things, less incline for similar speed which allows for a generally more normal gait, they still have a noticeable problem. In order to prevent the user from having to alter their stride unnaturally to accelerate the belt beyond a speed easily obtained by a preset incline, the user is required to pump the arm members harder and faster. For many users, this is not a problem, and provides for a natural motion because as they increase in running speed, their arms naturally reciprocate faster to balance. For some, however, particularly those with less upper body strength, the acceleration's necessarily increased demand on the upper body can be undesirable. Because of the reliance on the limits of propulsive force of the upper extremities and the requirements of most users, the belt speed may again become dependent on the user's rearward force.
This problem is still further exaggerated when the treadmill is at a low angle of incline, the user's weight is pressing the belt into the platform over which it is supported and little of the user's weight serves to help move the belt as it would if the belt was at a higher incline, therefore there is a much greater frictional and inertial component which must be overcome to move the belt than when the belt is at a steeper incline. Further, generally a user will wish to start exercising with the belt at a low angle of incline and with a slower speed as that is generally considered a less rigorous exercise and provides for a warm-up period.
The inertial component at the start of the exercise and the need for increased arm drive and upper body workout to increase speed are one of the concerns with an arm driven motorless treadmill. Another is that the steeper the incline of the treadmill and the heavier the user, the easier it is to move the belt. This, sometimes, can create problems where the exercise is undesirably fast. Many modern users like to increase incline as a way of making the exercise more difficult without necessarily having to run on the treadmill. With a motorless arm powered treadmill, however, for some individuals the belt can actually move too easily when the platform is greatly inclined forcing the user to have to run to keep up with the change in incline when they would prefer to move slower at the higher incline. For a heavier individual, the belt can be acted upon by significant force just from the weight of the individual which can result in the user needing to run at an undesirably high speed to keep from falling off the treadmill. Therefore, at a high incline, the user may also be moving faster than desired during the exercise.